Analog digital cascade converter

Abstract

In an analog-digital converter working at microwave frequencies, the input signal is addressed in parallel to bit levels which are in cascade with one another. Each bit level has a transducer which converts the voltage into a current, and compares this current with a calibrated source. The resultant current is addressed to a logic circuit, the output of which delivers a bit. An intermediate output of the logic circuit constitutes a control signal which regulates the currents of the analog comparators of the less significant bit levels. The calibrated currents are in geometrical progression.

What is claimed is: 
     
       1. An analog-digital converter converting an input analog signal into an output digital signal formed by several bits, wherein the input signal is addressed in parallel to one and the same set of several bit level circuits connected with one another in cascade, each level being formed by: a transducer stage which converts the input voltage into a current which is proportionate to it,   an analog comparator stage which compares said current with a calibrated current given by several elementary current sources,   a logic circuit stage, a first output of which gives a control signal applied to the elementary current sources of the less significant bit levels, and a second output which delivers a bit of the digital signal.   
     
     
       2. An analog-digital converter according to claim 1 wherein, at each bit level, the calibrated current of the analog comparator is given by a series of elementary current sources, the delivered currents of which are in geometrical progression 2 n  I o , the first of the current sources in the series, for each bit level, being not controlled, and the following current sources being each controlled by a transistor which is itself controlled by the signal of the first output of a logic circuit of a more significant bit level. 
     
     
       3. An analog-digital converter according to claim 2, wherein the non-controlled elementary current sources deliver currents in geometrical progression from the least significant bit level up to the most significant bit level, the least significant bit level being assigned the order zero in the geometrical progression s n  I o  (2 o  I o  = I o ). 
     
     
       4. A converter according to claim 1 wherein: the transducer stage has a transistor connected to a transistor of the logic circuit stage such that only two transistor junctions exist between input Ve and output So.   
     
     
       5. An analog-digital converter converting an input analog signal into an output digital signal formed by several bits, wherein the input signal is addressed in parallel to one and the same set of several bit level circuits connected with one another in cascade, each level being formed by: a transducer stage which converts the input voltage into a current which is proportionate to it,   an analog comparator stage which compares said current with a calibrated current given by several elementary current sources,   a logic circuit stage, a first output of which gives a control signal applied to the elementary current sources of the less significant bit levels, and a second output which delivers a bit of the digital signal; and   wherein, for each bit level, the logic circuit stage comprises: an inverter formed by a first transistor powered by a current source, the output signal of the analog comparator being applied to the gate of the first transistor;   a follower formed by a second transistor, in parallel with the first transistor and in series with a third transistor mounted as a follower source, the gate of which is controlled by the first output of the inverter, which also gives the control signal to the analog comparators of the less significant bit levels; and   the second output of the logic circuit stage is taken from the source of the third transistor and giving a bit of the digital signal.     
     
     
       6. An analog-digital converter according to claim 5, wherein the first, second and third transistors o the logic circuit stage are of the normally off type, with positive threshold voltage. 
     
     
       7. An analog-digital converter converting an input analog signal into an output digital signal formed by several bits, wherein the input signal is addressed in parallel to one and the same set of several bit level circuits connected with one another in cascade, each level being formed by: a transducer stage which converts the input voltage into a current which is proportionate to it,   an analog comparator stage which compares said current with a calibrated current given by several elementary current sources,   a logic circuit stage, a first output of which gives a control signal applied to the elementary current sources of the less significant bit levels, and a second output which delivers a bit of the digital signal;   wherein, at each bit level, the calibrated current of the analog comparator stage is given by a series of elementary current sources, the delivered currents of which are in geometrical progression 2 n  I o , the first of the current sources in the series, for each bit level, being not controlled, and the following current sources being each controlled by a control transistor which is itself controlled by the signal of the first output of a logic circuit of a more significant bit level; and   wherein the control transistors of the controlled current sources being of the normally off type, a voltage shifting diode is introduced between each control transistor and the current source which is controlled in order to turn each control transistor off, should the level level of the control signal be slightly positive.   
     
     
       8. An analog-digital converter converting an input analog signal into an output digital signal formed by several bits, wherein the input signal is addressed in parallel to one and the same set of several bit level circuits connected with one another in cascade, each level being formed by: a transducer stage which converts the input voltage into a current which si proportionate to it,   an analog comparator stage which compares said current with a calibrated current given by several elementary current sources,   a logic circuit stage, a first output of which gives a control signal applied to the elementary current sources of the less significant bit levels, and a second output which delivers a bit of the digital signal; and   wherein, in order to obtain a large number of bits for the output digital signal, and to increase the precision of each bit level, a voltage shifting stage is introduced between the analog comparator stage and the logic circuit stage for each bit level.   
     
     
       9. An analog-digital converter converting an input analog signal into an output digital signal formed by several bits, wherein the input signal is addressed in parallel to one and the same set of several bit level circuits connected with one another in cascade, each level being formed by: transducer and analog comparator means for converting the input voltage into a proportionate current and for comparing the current with a calibrated current given a plurality of elementary current sources; and   logic comparator means connected to said transducer and analog comparator means, said logic comparator means comprising a direct coupled FET logic circuit having two outputs; and   wherein a first output of the direct coupled FET logic circuit applies a control signal to the plurality of elementary current sources of the less significant bit levels and a second output delivers a bit of the output digital signal.